The combination of RF transverse gas electric discharging technology with optical waveguide technology drives the rapid development of waveguide CO2 laser technology. In the past decade, RF transverse single waveguide CO2 laser technology has experienced a development process from all-ceramic waveguide structures to ceramics and metal sandwich waveguide structures to all-metal waveguide structures. In the all-ceramic waveguide structure (see FIG. 1A), a square waveguide is composed of two vacuum ceramic side walls 33 and two vacuum ceramic clamp plates 34, and disposed between two metal electrodes 32 connected with a high frequency power supply 31. A gain channel area is formed in the waveguide by discharge excitation. The advantage of the all-ceramic waveguide structure is low loss of optical wave. Along with the development of the waveguide CO2 laser technology, in order to enhance gain cooling effect, decrease the cost and simplify the structure, the metal and ceramic sandwich waveguide structure is proposed (see FIG. 1B). In the metal and ceramic waveguide structure, two metal electrodes 32 and two vacuum ceramic side walls 33 form a waveguide discharge excitation channel, the metal electrodes 32 being connected with the high frequency power supply 31. In order to further lower the cost of device and facilitate modularization of production, in 1988 Synrad company of the USA proposed an RF excitation large aperture all-metal channel CO2 laser technology, disclosed on Laser Focus, pp 44–48, April 1998 (see FIG. 1C). In the technology, a gas discharge channel is composed of two metal side walls 36 having surface insulation layers and two metal electrodes 37 of having surface insulation layers. The metal side walls 36 having the surface insulation layers are connected with a metal housing 35. The two metal electrodes 37 having surface insulation layers are connected with the high frequency power supply 31. The two metal electrodes 37 have a phase difference of 180 degree, forming a four-electrode discharging mode. In 1991, Mr. Jianguo Xin, et al. from Beijing Institute of Technology developed a two-electrode RF transverse excited all-metal waveguide structure CO2 laser technology, disclosed on Applied Physics Letters, Vol. 59(26), p3363, 1991 (see FIG. 1D). In this kind of structure, two metal electrodes 32 and two metal side walls 36 with surface insulation layers form a gas discharge channel of a waveguide. A 0.1 mm thick gas gap exists between the metal side walls 36 with two surface insulation layers and the metal electrodes 32. According to Paschen's law, the gas breakdown voltage in a very small gas gap is relatively high, and the voltage in the air gap is only ½ of the voltage between the two metal electrodes 32. Therefore gas discharge excitation can be limited to within the waveguide channel by appropriately designing the size of waveguide channel.
In present there are only two institutes in the world which are reported to own RF excited all-metal CO2 laser technology: the RF excited four-electrode large aperture all-metal channel CO2 laser from Synrad Company of the USA, and the RF transverse excited two-electrode all-metal waveguide structure CO2 laser.
But by far, all of the area scaling slab waveguide RF excited diffusively cooled CO2 lasers reported home and abroad adopt a metal and ceramic sandwich structure. In a technical point of view, the waveguide RF excited diffusively cooled CO2 laser with the metal and ceramic sandwich structure uses ceramics to electrically separate discharge electrodes so as to generate gas discharge to form a gain area in the waveguide of the metal and ceramic sandwich structure. The process of this kind of metal and ceramic sandwich structure is relatively complex and higher manufacturing cost. On the other hand, the RF excited diffusively cooled CO2 laser with all-metal waveguide structure uses Paschen's law of gas discharge and principle of voltage division 1 to suppress the gas discharge inside the all-metal waveguide to form a gain area. The principle of forming gain area in the two kinds of technologies is different.
All of the prior structures of slab waveguide lasers are of two dimensional waveguide structures. In the prior two dimensional slab waveguide structure, a high order mode effect in the waveguide can be generated in the direction parallel with the electrodes in the waveguide cross section, making the intensity of laser output beam distributed in the direction to be modulated, thereby affecting the beam quality.